Microstructure characterisation and mechanical properties of a functionally-graded NbC/high chromium white cast iron composite

Abstract

A functionally graded NbChigh chromium white cast iron composite was successfully fabricated by centrifugal casting for high wear applications. The migration of primary NbC particles to the outer periphery, as predicted by Stokes' law, resulted in an extremely hard outer layer at the surface of a softer bulk material. Microstructural characterisation showed that both the volume fraction and the morphology of the carbides varies along the thickness of the specimen. At the outer surface, the NbC was present as primary carbides while Chinese-script NbC was found in the bulk of the material. Hardness, sliding wear and three-point bending tests confirmed that the outer layer was harder and more wear resistant than the rest of the material, which was correspondingly tougher. The study of the fracture surface of the specimens showed that there is a strong bond between NbC and the matrix such that delamination between the reinforcements and the matrix did not occur during fracture. If Chinese-script NbC can be reduced or prevented in the bulk material, further improvements to toughness could be achieved.

Fracture toughness testing using photogrammetry and digital image correlation

“…A comparison between the expected fracture toughness results in Table 1 and the actual fracture toughness results reported in Table 2 shows that the hard layer performed below expectations while the bulk material performed within the expected range. A detailed explanation for this, based on detailed fracture surface analysis and microstructural characterisation, is also provided in the study of the parent material from which the specimens were obtained from [ 18 ]. What is important, however, is that the fracture toughness results of both the hard layer and the bulk material, as calculated using the proposed DIC and photogrammetry technique, were consistent with those of traditional high chromium white cast iron alloys (20 MPa to 33 MPa as reported earlier).…”

“…In summary, this mechanical test requires the fabrication of fatigue pre-cracked notched specimens. A detailed study of the investigated material is reported elsewhere [ 18 ], but all relevant information pertaining to this study (namely, a summary of the material and the three-point bending test procedures and results) will be detailed here. The schematic of the three-point bending set-up is shown in Fig.…”

“…The material investigated in this study is a high chromium white cast iron alloy that was further reinforced with niobium carbide. Centrifugal casting was used to the segregate niobium carbide particles toward the outer periphery of the casting in order to create a functionally graded material where the outer surface was harder and more wear resistant (herein referred to as the hard layer) while the bulk material was softer and tougher [ 18 ]. As such, the three-point bend specimens were extracted from these two distinct regions of this functionally graded casting, as was reported in the quoted study.…”

The Influence of Microstructure on Abrasive Wear Micro-Mechanisms of the Claddings Produced by Welding Used in Agricultural Soil

“…However, due to their higher dispersion and lower fraction, when compared to layer I, they did not cause increased micro-delamination. This layer (Figure 12b) was dominated by the micro-cutting mechanism (scratches), and the niobium carbides firmly embedded in the eutectic matrix were visible, which, similar to work [36], inhibited abrasive wear. The favorable effect of NbC on abrasive wear was also confirmed in [20][21][22][23]37].…”

Experimental Study on the Effect of Gradient Interface on the Mechanical Properties of Cu/WCP Functionally Gradient Materials Using Digital Image Correlation Technique

“…Compared with the complex preparation process of continuous gradient materials, the metal-based functionally gradient composites with relatively simple preparation process [ 15 ] will be one of the development directions of laminated gradient materials. Metal-based functionally gradient composites have specific positional properties in components, in addition to performing their specific properties, metal-based functionally gradient composites are often required to withstand high stress or load in structures or components.…”